Various types of screening devices for rain gutters have been previously known but have been largely unsuccessful because of various shortcomings. In general, such devices have been provided with relatively large openings to increase the possibilities that water flowing from a roof will fall through the screen into a gutter rather than overflowing the screen as a fluid sheet during a heavy downpour. However, screens with openings large enough to reduce the possibilities of such overflow also tend to be large enough to snare leaves and other debris, thereby negating or reducing the usefulness of the screens and, because of the additional structure, increasing the problems of gutter cleaning and maintenance that such systems are intended to avoid. In an effort to overcome some of these problems, hinged gutter guards have been devised as disclosed, for example, in U.S. Pat. Nos. 2,072,415, 4,032,456, 2,841,100, 4,351,134 and 3,420,378. Such systems only serve to reduce, not eliminate, the inconveniences of gutter cleaning and, because of their complexity, are usually more expensive to purchase, install, and maintain than simpler arrangements. Other patents illustrating the state of the art are U.S. Pat. Nos. 2,271,081, 4,769,957, 4,866,890, 3,053,393 and published United Kingdom application GB 2,218,828A.
An importance aspect of this invention lies in the discovery that a highly effective and relatively inexpensive gutter screening system may be achieved if the apertures of a screen are relatively small and are of rectangular shape, and if the ribs and bars defining such apertures are dimensioned and arranged, first, to direct or channel the flow of water along the screen in the direction of roof slope and, second, to interrupt the directed flow, breaking surface tension and deflecting the water through the screen apertures and into the gutter. Because of the small size of such apertures, and because the flow-directing ribs protrude well above the transverse flow-interrupting bars of the screen, leaves and twigs are unlikely to become entrapped or restrained. At the same time, the construction and arrangement of flow-directing ribs and flow-interrupting bars promotes the flow of rain water into a gutter despite the relatively small dimensions of the apertures.
The screen is mounted so that its upper portion assumes the same slope as that of the roof. The remainder of the screen overlying the gutter may continue downwardly following generally the same slope, although it has been found that in most cases the standard mounting of a gutter results in a gentle curvature of that portion of the screen overlying the gutter opening with the outer edge of the screen assuming a generally horizontal condition where it is supported upon the outer edge or flange of the gutter. The tensioned condition of the screen caused by such curvature tends to keep its outer edge portion in forceful contact with the gutter's outer flange, although it is preferred that the outer portion of the screen be securely clamped in position by suitable attachment means. Such attachment means may take the form of an L-shaped clamping strip secured by nylon press studs or rivets to the outer flange of the gutter.
The rectangular apertures or openings of the screen are elongated in directions parallel with a gutter with each aperture having an area within the general range of 4 to 30 square millimeters. A preferred range is 5 to 20 square millimeters, with particularly effective results being obtained with areas of about 10 square millimeters. The optional dimensions of each aperture are believed to be approximately 5 millimeters in length and 2 millimeters in width, although variations (with decreasing effectiveness) may be achieved with lengths falling within the general range of 4 to 10 millimeters and widths of 1 to 3 millimeters. The undersurfaces of the flow-directing ribs and flow-interrupting bars are generally coplanar but the height of the ribs should be approximately 40 to 100 percent greater than the height of the bars. Other significant dimensions believed to be of lesser importance are detailed in the specification, and additional features, objects, and advantages of the invention will become apparent from the specification and drawings.